Telescopic systems, such as spotting scopes and riflescopes, as well as astronomical and other telescope systems, typically do not have very close focus capability since this is not a requirement for the intended use of the device. For example, many astronomical telescopes cannot be focused on targets that are closer than several meters away. Likewise many spotting scopes used for various sport, hobby, and commercial applications lack close focus ability. Another telescope device is a riflescope. These are frequently designed to focus from infinity to about 50 meters and typically have only a very limited ability to adjust the focus. Even specialty rifle scopes which have adjustable objective lenses are not designed to focus on nearby targets only a few meters away.
As a result, these telescopes cannot be used for applications in which a close focus capability is needed. Such close focus applications may include visual close-ups of nearby birds, insect studies in the field, and close inspection of equipment in nearby hazardous or inaccessible environments. In addition, the lack of a close focus capability makes testing or training uses of the telescope more cumbersome since a target placed nearby cannot be brought into focus. One example is telescopic photography system testing during which the optical system must be focused on a target. A different example is marksman “dry-fire” training during which various aspects of riflery can be practiced, such as trigger training during which a marksman observes the target through the scope while pulling the trigger to try and minimize the motion of the gun. The lack of a close-focus capability limits indoor applicant and training uses because many indoor facilities do not have very a long clear line of sight where the telescope and target can be set up. Similarly, the lack of a close-focus capability may prevent repurposing of existing telescope equipment for alternative applications requiring a close-focus.
It is known to use a fixed single-element conversion lens attached to the front of a conventional camera lens to increase or decrease the lens' focal length and allow for an increased zoom capability, such as a 2× tele-converter for converting a 3× zoom to a 6× zoom lens or a 0.5× wide angle converter providing a wide angle or even a “fisheye” field of view. However, it is not always desired to substantially alter the magnification or field of view of a lens system. Accordingly, it would be beneficial to provide an optical macro adaptor which can be coupled to the objective end of a telescope and provide the telescope system with a closer than normal telescopic focus range while preserving the telescope's magnification and field of view.
It is known to attach a single lens stopped down by about ⅔ of its diameter to the front of rifle scope to provide for a limited close-focus capability. The stopping is a conventional way to avoid introducing optical aberrations which would otherwise be caused by the portions of the lens far from its optical center. The extensive stopping provides a significant reduction in light gathering capability. As a result, this lens is suitable for use only in very bright conditions.
It would be a further benefit to provide an adaptor that introduced minimal optical aberrations without requiring the lenses in the adaptors to be stopped down so that as much of the telescope's original aperture as possible can be utilized.
It would be a further benefit if such an adaptor itself could be focused to provide additional flexibility of the telescope system in close-focus applications.